WO2021196078A1 - Device and method for regulating and controlling polarization state of light beam - Google Patents

Abstract

A device and method for regulating and controlling the polarization state of a light beam, the device comprising a polarizing sheet (1), a phase plate (2), a 4f optical system (3), a polarization converter (4), a first objective lens (5), a low-pass filter (6) and a second objective lens (7) which are arranged in sequence. The polarizing sheet (1), the phase plate (2), the 4f optical system (3), the polarization converter (4), the first objective lens (5), the low-pass filter (6) and the second objective lens (7) share a central axis; the 4f optical system (3) comprises a first lens (8) and a second lens (9); the phase plate (2) is located on a front focal plane of the first lens (8), the polarization converter (4) is located on a rear focal plane of the second lens (9), and the low-pass filter (6) is located on a rear focal plane of the first lens (5). One-to-one correspondence between phase and polarization is utilized, and the control over the polarization state of a light beam is directly completed by means of phase regulation and control. Since real-time dynamic pixelation control over the phase of the light beam may be achieved by means of a phase control device, not only can real-time control of polarization dynamics be achieved, and the precision of polarization regulation and control may reach the level of a single pixel.

Description

Device and method for adjusting and controlling polarization state of light beam Technical field

The invention relates to the field of optics, in particular to a device and method for adjusting and controlling the polarization state of a light beam.

Background technique

Amplitude, phase, and polarization are the three natural attributes of light beams. Through the development of tourism, the study of the three has not only deepened people's understanding of the behavior of light beams, but also caused great breakthroughs in the field of optics. In the past few centuries, people have witnessed the great success of scalar optics with amplitude and phase control as the core. Benefiting from mature amplitude and phase control technologies, researchers have created many optical applications based on scalar optics theory, such as free-space optical communications, optical tweezers, photolithography, optical imaging, holographic displays, and so on. These optical applications have greatly changed people's lifestyles and significantly improved people's living standards.

However, as a stage of optical development, the limitations of scalar optics have slowly emerged. For example, although Wang Jian and others proposed the use of orbital angular momentum multiplexing and demultiplexing technology to achieve a breakthrough expansion of communication capacity, reaching 1.37Tb/s (refer to J. Wang, Jeng-Yuan Yang, et al, Terabit free-space data transmission employing orbital angular momentum multiplexing, Nature Photonics, 2012, 6, 488-496), but it is almost impossible to further increase the information capacity of light wave transmission, unless a vector beam with a special polarization mode is used as an information carrier (see literature "4x 20Gbit/s mode division multiplexing over free space using vector modes and a q-plate mode(de)multiplexer" Optics Letters. 40(9), 1980-1983 (2015).). In terms of lithography research, polarization optimization control has been proven to further improve the resolution of lithography (see the document "Source mask polarization optimization" Journal of Micro/Nanolithography, MEMS, and MOEMS. 10(3), 1-10 (2011) ).). There is no doubt that the development trend of optics is bound to move from scalar optics to vector optics, and now is only the beginning of vector optics. The key to turning on vector optics is to achieve real-time dynamic pixel-level polarization control of the beam.

Generally, based on the principle that two orthogonally polarized light beams are superimposed on each other, the polarization state of the light beam can be controlled. For example, the superposition of left and right circularly polarized beams with different phases or the superposition of horizontal and vertical linear polarized beams can generate special vector beams (see the document "Generation of arbitrary vector beams with a spatial light modulator and a common path interferometric arrangement" Optics Letters. 32(24), 3549-3551(2007).). However, this method has the following shortcomings: First, the two-beam coherent superposition requires a precise interference optical path, which greatly increases the difficulty of the application of this method; second, the phases of the two orthogonal beams need to be controlled independently, which requires Complex algorithms are not conducive to pixel-level polarization control; third, the energy utilization rate is low, generally not exceeding 10%. Although the polarization converter based on the geometric phase principle can achieve more than 90% energy utilization, because the polarization converter can only directly convert horizontal or vertical linearly polarized light into spatially varying linearly polarized light, we It is impossible to generate a vector beam with both a circular polarization state and a linear polarization state from this kind of polarization converter (see the literature "Optical spin-to-orbital angular momentum conversion in inhomogeneous anisotropic media" Physical Review Letters.96(16), 163905 (2006).). This further illustrates that the polarization converter based on geometric phase cannot achieve arbitrary polarization control. In order to achieve the full polarization control of the beam, the researchers used the metasurface structure design method to achieve the generation of arbitrary polarization vector beams, and the energy utilization rate was greater than 70% (see the document "Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission"Nature Nanotechnology.10(11),(2015).). Nevertheless, the design and processing of the metasurface structure is very difficult, the technical requirements are extremely high, the cost of processing large-size devices is extremely expensive, and dynamic real-time variable polarization control cannot be achieved.

Technical solutions

The purpose of the present invention is to provide a light beam polarization state control device and method aiming at the shortcomings and difficulties of the prior art, aiming to provide a simple beam control device to realize dynamic real-time pixel-level control of the light beam polarization state.

In order to achieve the above objective, the present invention provides a light beam polarization state control device. The light beam polarization state control device includes: a polarizer, a phase plate, a 4f optical system, a polarization converter, a first objective lens, and a low pass arranged in sequence. The filter and the second objective lens, the polarizer, the phase plate, the 4f optical system, the polarization converter, the first objective lens, the low-pass filter and the second objective lens share a central axis;

The 4f optical system includes a first lens and a second lens, the phase plate is located on the front focal plane of the first lens, the polarization converter is located on the back focal plane of the second lens, and the low-pass filter Located at the back focal plane of the first objective lens;

The external light is converted into horizontal linearly polarized light through the polarizer, and enters the phase plate;

The phase plate adjusts the phase of the linearly polarized light into a phase distribution of φ, and passes through the 4f optical system and then enters the polarization converter vertically to obtain the linearly polarized light whose phase is φ and its polarization state is spatially changed. The electric field distribution is expressed as:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor;

Is the generalized phase distribution,

Are the convergence angle and the azimuth angle of the first objective lens, and β ₀ is the polarization control factor;

The linearly polarized light whose phase is φ and whose polarization state is spatially changed passes through the first objective lens and is decomposed into a first electric field component E _inner focused beam and a second electric field component E _outer focused beam, which can be expressed as

Among them, <L> and <R> represent the left and right circular polarization modes respectively;

The first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component E _outer focused beam is filtered out, thereby obtaining the first electric field component E _inner focused beam;

The focused light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution.

Optionally, the phase plate is obtained by encoding or processing and coating with a phase spatial light modulator.

Optionally, the generalized phase distribution

_{The first electric field component E inner} focused beam and the second electric field component E _outer focused beam of the linearly polarized light whose phase is φ and its polarization state changes spatially through the first objective lens are spatially separated in the focal area of the first objective lens.

Optionally, the distance between the first lens and the second lens is the sum of their focal lengths.

Optionally, the distance between the first objective lens and the second objective lens is the sum of the focal lengths of the two.

Optionally, the polarization converter is a liquid crystal polarization control polarization converter.

Optionally, the transmittance of the low-pass filter is expressed as:

Among them, r ₀ is the effective aperture radius of the low-pass filter.

In order to achieve the above objective, the present invention also provides a method for adjusting the polarization state of a light beam. The adjusting method is applied to the adjusting device described above, and the adjusting method includes:

The external light is converted into horizontal linearly polarized light through the polarizer and enters the phase plate;

The phase of the linearly polarized light is adjusted to a phase distribution of φ through the phase plate, and is perpendicularly incident to the polarization converter after passing through the 4f optical system to obtain the linearly polarized light whose phase is φ and its polarization state is spatially changed, The electric field distribution is:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor;

Is the generalized phase distribution,

Are the convergence angle and the azimuth angle of the first objective lens, and β ₀ is the polarization control factor;

The linearly polarized light whose phase is φ and whose polarization state is spatially changed passes through the first objective lens and is decomposed into a first electric field component E _inner focused beam and a second electric field component E _outer focused beam, which can be expressed as

Among them, <L> and <R> represent the left and right circular polarization modes respectively;

The first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component E _outer focused beam is filtered out, thereby obtaining the first electric field component E _inner focused beam;

The focused light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution.

Optionally, the generalized phase distribution

_{The first electric field component E inner} focused beam and the second electric field component E _outer focused beam of the linearly polarized light whose phase is φ and its polarization state changes spatially through the first objective lens are spatially separated in the focal area of the first objective lens.

Optionally, the transmittance of the low-pass filter is expressed as:

Among them, r ₀ is the effective aperture radius of the low-pass filter.

Optionally, the polarization converter is a liquid crystal polarization control polarization converter.

The device and method for adjusting the polarization state of a beam provided by the present invention include: a polarizer, a phase plate, a 4f optical system, a polarization converter, a first objective lens, a low-pass filter, and The second objective lens, the polarizer, the phase plate, the 4f optical system, the polarization converter, the first objective lens, the low-pass filter and the second objective lens share a central axis, and the 4f optical system includes a first lens and a second lens , The phase plate is located at the front focal plane of the first lens, the polarization converter is located at the rear focal plane of the second lens, and the low-pass filter is located at the rear focal plane of the first objective lens; external light passes through The polarizer is converted into horizontal linearly polarized light and enters the phase plate; the phase plate adjusts the phase of the linearly polarized light into a phase distribution of φ, and enters the polarization conversion vertically after passing through the 4f optical system The electric field distribution is as follows:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor,

Is the generalized phase distribution,

Are the convergence angle and the azimuth angle of the first objective lens, β ₀ is the polarization control factor; the linearly polarized light whose phase is φ and its polarization state is spatially changed passes through the first objective lens, and is decomposed into the first electric field component E _inner focusing The beam and the second electric field component E _outer focused beam can be expressed as

Wherein, <L> and <R> represent left and right circular polarization modes respectively; the first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component The E _outer focused light beam is filtered out to obtain the first electric field component E _inner focused light beam; the first electric field component E _inner focused light beam passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution. This application uses the one-to-one correspondence between the phase and the polarization, and directly controls the polarization state of the beam through the adjustment of the phase. Because the phase of the light beam can be controlled by real-time dynamic pixelation using a phase control device, such as a phase spatial light modulator, the pixelated phase will inevitably produce a pixelated polarization output. Therefore, the present invention can not only achieve real-time dynamic control of polarization, but also The precision of polarization control can reach a single pixel.

Description of the drawings

FIG. 1 is a schematic structural diagram of a first embodiment of a device for adjusting and controlling the polarization state of a light beam according to the present invention;

2 is a schematic diagram of a detailed structure of the 4f optical system in the embodiment of the present invention;

3a is a schematic diagram of the total light intensity distribution of spatially varying linearly polarized light emitted by the polarization converter in the embodiment of the present invention;

3b is a light intensity distribution diagram of the spatially varying linearly polarized light emitted by the polarization converter in the embodiment of the present invention after passing through the polarizer;

Fig. 4 is a schematic diagram of a low-pass filter in an embodiment of the present invention;

5 is an experimental result diagram of light beams with different polarization distributions generated by phase plates with different phase distributions in an embodiment of the present invention;

6 is another experimental result diagram of light beams with different polarization distributions generated by phase plates with different phase distributions in the embodiment of the present invention.

Embodiments of the present invention

It should be understood that the specific embodiments described here are only used to explain the present invention, but not used to limit the present invention.

1, in the first embodiment of the light beam polarization state control device of the present invention, the light beam polarization state control device includes: a polarizer 1, a phase plate 2, a 4f optical system 3, and a polarization converter arranged in sequence 4. The first objective lens 5, the low-pass filter 6 and the second objective lens 7, the polarizer 1, the phase plate 2, the 4f optical system 3, the polarization converter 4, the first objective lens 5, the low-pass filter 6 and the second objective lens The two objective lenses 7 share a central axis,

The 4f optical system 3 includes a first lens 8 and a second lens 9, the phase plate 2 is located on the front focal plane of the first lens 8, and the polarization converter 4 is located on the back focal plane of the second lens 9;

The low-pass filter 6 is located on the back focal plane of the first objective lens 5;

The incident light beam enters the polarizer 1 vertically, and sequentially passes through the phase plate 2, the 4f optical system 3, the polarization converter 4, the objective lens 5, the low-pass filter 6, and the objective lens 7, and finally exits the desired polarization distribution beam from the objective lens 7. The polarizer 1, the phase plate 2, the 4f optical system 3, the polarization converter 4, the objective lenses 5, 7, and the low-pass filter 6 share a central axis. For ease of understanding, an example is provided for explanation:

The incident light is a linearly polarized beam with a diameter of 4mm and a wavelength of 633nm. Beams of other wavelengths can be used for specific implementation;

Polarizer 1 is a polarizer with a wavelength of 633nm for incident light, or a broadband polarizer with a working wavelength of 633nm; its polarization direction is the horizontal direction;

Phase plate 2 adopts phase-type spatial light modulation for encoding realization or direct processing and coating realization, and other realization methods can also be used; its phase parameter

in,

Is the azimuth angle of the first objective lens 5, m=30, and can be other values in specific implementation;

4f optical system 3 is realized by lenses 8, 9 with a focal length of 100mm, and the distance between lenses 8, 9 is 200mm;

The polarization converter 4 adopts Q-plate or other implementation methods. _{The polarization parameter β 0} =0 of the beam emitted by the polarization converter 4,

in

Is the azimuth angle of the first objective lens 5, m=30;

The numerical apertures of the objective lenses 5 and 7 are both 0.01, and the apertures can also be other values in specific implementation;

The low-pass filter 6 is implemented by a pinhole or diaphragm _{with an effective clear aperture radius r 0 =400 μm.}

As shown in Figure 1, the incident light is a linearly polarized beam with a diameter of 4mm and a wavelength of 633nm. After passing through the polarizer 1, rotate the polarizer so that the polarizing direction of the polarizer is horizontal, and the beam exiting from the polarizer is horizontal Of linearly polarized light.

The phase of phase plate 2 is expressed as

Among them, phase represents the function of extracting the phase; i is an imaginary number;

Is a constant factor; in this embodiment, m=30; β is a phase control factor. As shown in Fig. 1, the phase plate 2 and the polarizer 1 share a central axis. After the horizontal linearly polarized light beam emitted by the polarizer passes through the phase plate 2, the phase of the light beam becomes a phase distribution of φ. At this point, by adjusting the parameters of the phase plate

And β realize the control of the phase of the horizontally polarized beam emitted from the phase plate.

As shown in FIG. 2, the 4f optical system 3 is composed of a lens 8 and a lens 9. In this embodiment, the focal lengths of the lens 8 and the lens 9 are both 100 mm, the distance between the two is 200 mm, and they share a central axis with the polarizer. Since the phase plate 2 is located on the front focal plane of the lens 8 in the 4f optical system, the phase φ of the phase plate can be projected onto the back focal plane of the lens 9 in the 4f optical system.

The polarization converter 4 shares a central axis with the polarizer 1 and is located on the back focal plane of the lens 9 in the 4f optical system. In this embodiment, the polarization converter 4 is implemented by Q-plate. The horizontal linearly polarized light emitted by the 4f optical system 3 is incident perpendicularly to the polarization converter 4. Due to the polarization and phase control of the polarization converter 4 and the phase plate 3, the light beam emitted from the polarization converter 4 can be expressed as:

Among them, i is an imaginary number; φ is the phase of the phase plate 2; β ₀ is the light polarization control factor. In this embodiment, β ₀ =0. It can be seen from the outgoing beam E of the polarization converter 4 that the beam not only has the phase φ of the phase plate 2, but also has a linearly polarized light whose polarization state changes in space.

The objective lens 5 shares a central axis with the polarizer 1, and its numerical aperture is 0.01. The spatially varying linearly polarized light beam emitted from the polarization converter 4 is focused by the objective lens 5. The focused light beam in the focal area of the objective lens 5 can be expressed as E = E _inner + E _outer , E _inner and E _outer are respectively:

Among them, <L> and <R> respectively represent left and right circular polarization modes; in this embodiment, m=30.

As shown in FIG. 1, a low-pass filter 6 is placed on the focal plane of the objective lens 5. The low-pass filter 6 and the polarizer 1 share a central axis. The focused light beam emitted by the objective lens 5 can be decomposed into two electric field components E _inner and E _outer . Since the electric field components E _inner and E _outer are respectively located at different spatial positions of the focal plane of the objective lens 5, when the focused light beam emitted by the objective lens 5 E = E _inner + E _{outer is} incident on the low-pass filter with the effective clear aperture radius r _{0 =400 μm} At the time of _{filter 6, E outer} is filtered out, and the focused light beam emitted from the low-pass filter 6 is E _inner . Since the electric field components E _inner and E _outer are equal in size, after passing through the low-pass filter 6, the energy utilization rate of the optical system is 50%. In addition, the _{polarization distribution of E inner} only depends on the parameter of the phase φ of the phase plate 2

And β. In other words, by adjusting the phase φ of the phase plate 2, the electric field component E _inner of the focused beam can be controlled.

The objective lens 7 shares the aforementioned central axis, and its numerical aperture is the same as that of the objective lens 5, both of which are 0.01. _{After the focused light beam E inner} emitted by the low-pass filter 6 enters the objective lens 7, since the numerical apertures of the objective lenses 5 and 7 are equal, the objective lens 7 _{restores the focused light beam E inner} emitted by the low-pass filter 6 to a polarized light beam with a diameter of 4 mm . The polarized light beam emitted by the objective lens 7 is a restoration result of the _{focused light beam E inner emitted by the low-pass filter 6.} Since the polarization distribution of the focused beam E _inner only depends on the parameters in the phase φ of the phase plate 2

And β, therefore, the polarized light beam emitted by the objective lens 7 can be directly controlled by the phase φ of the phase plate 2. As shown in FIG. 5, different phases of the phase plate 2 can emit light beams with different polarization distributions from the objective lens 7. Specifically, when the phase distribution of the phase plate 2 is as shown in Fig. 5(a), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the vertical linearly polarized light beam in the square area; when the phase distribution of the phase plate 2 is as shown in Fig. 5(d) , The light beam emitted by the objective lens 7 is composed of the background right-handed circularly polarized light and the square area left-handed circularly polarized light; when the phase distribution of the phase plate 2 is shown in Figure 5(g), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the square area right Composed of circularly polarized beams. Figure 5 (b, e, h) is the total light intensity distribution of the outgoing beam in the above three cases. Figure 5 (c, f, i) are the light intensity distribution diagrams of the outgoing beam passing through the polarizer with the horizontal polarization direction and the quarter wave plate with the fast axis at 45 degrees from the horizontal direction in the above three cases. In practical applications, the phase φ of the phase plate 2 can be pixelated and dynamically controlled in real time through a phase spatial light modulator or other optical elements. If the phase of the square area in Figure 5 (a, d, g) is reduced to a single pixel, the polarization corresponding to the pixel will also change accordingly.

As another embodiment, the phase parameter

in,

Are the convergence angle and azimuth angle of the first objective lens 5, k=2π/λ, incident light wavelength λ=633nm, m=20, and the low-pass filter 6 adopts a pinhole or light _{with an effective clear aperture radius r 0 =310μm.} Lanna realized. The position of each component, as well as the light path passing direction and sequence are the same as those in the above embodiment, and will not be repeated here. As a result, as shown in FIG. 6, different phase plates 2 can emit light beams with different polarization distributions from the objective lens 7. Specifically, when the phase distribution of the phase plate 2 is as shown in Fig. 6(a), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the vertical linearly polarized light beam in the square area; when the phase distribution of the phase plate 2 is as shown in Fig. 6(d) , The light beam emitted by the objective lens 7 is composed of the background right-handed circularly polarized light and the square area left-handed circularly polarized light; when the phase distribution of the phase plate 2 is as shown in Figure 6(g), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the square area right Composed of circularly polarized beams. Figure 6 (b, e, h) is the total light intensity distribution of the outgoing beam in the above three cases. Figure 6 (c, f, i) is the light intensity distribution diagram of the outgoing beam passing through the polarizer with the horizontal polarization direction and the quarter wave plate with the fast axis at 45 degrees from the horizontal direction in the above three cases. In practical applications, the phase φ of the phase plate 2 can be pixelated and dynamically controlled in real time through a phase spatial light modulator or other optical elements. If the phase of the square area in Figure 6 (a, d, g) is reduced to a single pixel, the polarization corresponding to the pixel will also change accordingly.

The device and method for adjusting the polarization state of a beam provided by the present invention include: a polarizer, a phase plate, a 4f optical system, a polarization converter, a first objective lens, a low-pass filter, and The second objective lens, the polarizer, the phase plate, the 4f optical system, the polarization converter, the first objective lens, the low-pass filter and the second objective lens share a central axis, and the 4f optical system includes a first lens and a second lens , The phase plate is located on the front focal plane of the first lens, the polarization converter is located on the back focal plane of the second lens, and the low-pass filter is located on the back focal plane of the first objective lens; external light The linearly polarized light converted into the horizontal direction by the polarizer enters the phase plate; the phase plate adjusts the phase of the linearly polarized light into a phase distribution of φ, and enters the polarized light vertically after passing through the 4f optical system The converter obtains linearly polarized light whose phase is φ and its polarization state changes in space, and its electric field distribution is:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor; in this embodiment, β ₀ =0, m=30; the linearly polarized light whose phase is φ and its polarization state is spatially changed passes through the first objective lens and is decomposed into the first objective lens. The electric field component E _inner focused beam and the second electric field component E _outer focused beam, E _inner and E _outer are respectively:

Wherein, <L> and <R> represent the left and right circular polarization modes respectively; the first electric field component E _inner focused beam and the second electric field component E _outer focused beam perpendicularly enter the low-pass filter, and the second electric field The focused light beam of the component E _outer is filtered out to obtain the first electric field component E _inner light beam; the first electric field component E _inner light beam passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution. This application uses the one-to-one correspondence between the phase and the polarization, and directly controls the polarization state of the beam through the adjustment of the phase. Because the phase of the light beam can be controlled by real-time dynamic pixelation using a phase control device, such as a phase spatial light modulator, the pixelated phase will inevitably produce a pixelated polarization output. Therefore, the present invention can not only achieve real-time dynamic control of polarization, but also The precision of polarization control can reach a single pixel. This method not only achieves dynamic real-time pixel-level polarization control, but also has an energy utilization rate of up to 50%. Compared with the dual-beam coherent superposition method and metasurface design, and the polarization control method based on the geometric phase principle, the present invention also avoids high-precision interference systems, complex algorithms, expensive and precise processing, and the like.

The present invention also provides a method for adjusting the polarization state of a light beam, which is applied to the adjusting device as described in any one of the above, and the adjusting method includes:

S10, the external light is converted into horizontal linearly polarized light through the polarizer, and enters the phase plate;

S20: Adjust the phase of the linearly polarized light to a phase distribution of φ through the phase plate, and enter the polarization converter vertically after passing through the 4f optical system to obtain a linear polarization with a phase of φ and a spatially varying polarization state. Light, its electric field distribution is:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor; in this embodiment, β ₀ =0, m=30;

S30, the linearly polarized light whose phase is φ and whose polarization state is spatially changed passes through the first objective lens, and is decomposed into a first electric field component E _inner focused beam and a second electric field component E _outer focused beam, wherein,

S40, the first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component E _outer focused beam is filtered out, thereby obtaining the first electric field component E _inner beam;

S50, the light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution.

The device for adjusting the polarization state of the beam includes: a polarizing plate 1, a phase plate 2, a 4f optical system 3, a polarization converter 4, a first objective lens 5, a low-pass filter 6 and a second objective lens 7 arranged in sequence. The polarizing plate 1 , The phase plate 2, the 4f optical system 3, the polarization converter 4, the first objective lens 5, the low-pass filter 6, and the second objective lens 7 share a central axis,

The 4f optical system 3 includes a first lens 8 and a second lens 9, the phase plate 2 is located at the front focal plane of the first lens 8, and the polarization converter 4 is located at the back focal plane of the second lens 9, so The low-pass filter 6 is located on the back focal plane of the first objective lens 5;

The incident light beam enters the polarizer 1 vertically, and sequentially passes through the phase plate 2, the 4f optical system 3, the polarization converter 4, the objective lens 5, the low-pass filter 6, and the objective lens 7, and finally exits the desired polarization distribution beam from the objective lens 7. The polarizer 1, the phase plate 2, the 4f optical system 3, the polarization converter 4, the objective lenses 5, 7, and the low-pass filter 6 share a central axis. For ease of understanding, an example is provided for explanation:

The incident light is a linearly polarized beam with a diameter of 4mm and a wavelength of 633nm. Beams of other wavelengths can be used in specific implementations;

Polarizer 1 is a polarizer with a wavelength of 633nm for incident light, or a broadband polarizer with a working wavelength of 633nm; its polarization direction is the horizontal direction;

Phase plate 2 adopts phase-type spatial light modulation for encoding realization or direct processing and coating realization, and other realization methods can also be used; its phase parameter

in

Is the azimuth angle of the first objective lens 5, m=30, and can be other values in specific implementation;

4f optical system 3 is realized by lenses 8, 9 with a focal length of 100mm, and the distance between lenses 8, 9 is 200mm;

The polarization converter 4 adopts Q-plate or other implementation methods. Polarization parameters of the outgoing beam of polarization converter 4

And β ₀ =0, where m=30;

The numerical apertures of objective lenses 5 and 7 are both 0.01;

The low-pass filter 6 is implemented by a pinhole or diaphragm _{with an effective clear aperture radius r 0 =400 μm.}

As shown in Figure 1, the incident light is a linearly polarized beam with a diameter of 4mm and a wavelength of 633nm. After passing through the polarizer 1, rotate the polarizer 1 so that the polarization direction of the polarizer 1 is horizontal, and then the beam emerges from the polarizer 1 It is linearly polarized light in the horizontal direction.

The phase of phase plate 2 is expressed as

Among them, phase represents the function of extracting the phase; i is an imaginary number;

Is a constant factor; in this embodiment, m=30; β is a phase control factor. As shown in Fig. 1, the phase plate 2 and the polarizer 1 share a central axis. After the horizontal linearly polarized beam emitted by the polarizer passes through the phase plate 2, the phase of the beam becomes a phase distribution of φ. At this point, by adjusting the parameters of the phase plate

And β realize the control of the phase of the horizontally polarized beam emitted from the phase plate.

As shown in Fig. 2, the 4f optical system 3 is composed of lenses 8,9. In this embodiment, the focal lengths of the lenses 8, 9 are both 100 mm, the distance between the two lenses is 200 mm, and they share a central axis with the polarizer. Since the phase plate 2 is located on the front focal plane of the lens 8 in the 4f optical system 3, the phase φ of the phase plate can be projected onto the back focal plane of the lens 9 in the 4f optical system 3.

The polarization converter 4 shares a central axis with the polarizer 1 and is located on the back focal plane of the lens 9 in the 4f optical system 3. In this embodiment, the polarization converter 4 is implemented by Q-plate. The horizontal linearly polarized light emitted by the 4f optical system 3 is incident perpendicularly to the polarization converter 4. Due to the polarization and phase control of the polarization converter 4 and the phase plate 3, the light beam emitted from the polarization converter 4 can be expressed as:

Among them, i is an imaginary number; φ is the phase of the phase plate 2; β ₀ is the polarization control factor. In this embodiment, β ₀ =0. It can be seen from the outgoing beam E of the polarization converter 4 that the beam not only has the phase φ of the phase plate 2, but also has a linearly polarized light whose polarization state changes in space.

The objective lens 5 shares a central axis with the polarizer 1, and its numerical aperture is 0.01. The spatially varying linearly polarized light beam emitted from the polarization converter 4 is focused by the objective lens 5. The focused light beam in the focal area of the objective lens 5 can be expressed as E = E _inner + E _outer , where E _inner and E _outer are respectively:

In this embodiment, m=30.

As shown in FIG. 1, a low-pass filter 6 is placed on the focal plane of the objective lens 5. The low-pass filter 6 and the polarizer 1 share a central axis. The focused light beam emitted by the objective lens 5 can be decomposed into two electric field components E _inner and E _outer . Since the electric field components E _inner and E _outer are respectively located at different spatial positions of the focal plane of the objective lens 5, when the focused light beam emitted by the objective lens 5 E = E _inner + E _{outer is} incident on the low-pass filter with the effective clear aperture radius r _{0 =400 μm} At the time of _{filter 6, E outer} is filtered out, and the focused light beam emitted from the low-pass filter 6 is E _inner . Since the electric field components E _inner and E _outer are equal in size, after passing through the low-pass filter 6, the energy utilization rate of the optical system is 50%. In addition, since the _{polarization distribution of E inner} only depends on the parameter of the phase φ of the phase plate 2

_{Therefore, the electric field component E inner} of the focused beam can be controlled by adjusting the phase φ of the phase plate 2.

The objective lens 7 shares the aforementioned central axis, and its numerical aperture is the same as that of the objective lens 5, both of which are 0.01. _{After the focused light beam E inner} emitted by the low-pass filter 6 enters the objective lens 7, since the numerical apertures of the objective lenses 5 and 7 are equal, the objective lens 7 _{restores the focused light beam E inner} emitted by the low-pass filter 6 to a polarized light beam with a diameter of 4 mm . The polarized light beam emitted by the objective lens 7 is a restoration result of the _{focused light beam E inner emitted by the low-pass filter 6.} Since the polarization distribution of the focused beam E _inner only depends on the parameters in the phase φ of the phase plate 2

And β, therefore, the polarized light beam emitted by the objective lens 7 can be directly controlled by the phase φ of the phase plate 2. As shown in FIG. 5, different phases of the phase plate 2 can emit light beams with different polarization distributions from the objective lens 7. Specifically, when the phase distribution of the phase plate 2 is as shown in Fig. 5(a), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the vertical linearly polarized light beam in the square area; when the phase distribution of the phase plate 2 is as shown in Fig. 5(d) , The light beam emitted by the objective lens 7 is composed of the background right-handed circularly polarized light and the square area left-handed circularly polarized light; when the phase distribution of the phase plate 2 is shown in Figure 5(g), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the square area right Composed of circularly polarized beams. Figure 5 (b, e, h) is the total light intensity distribution of the outgoing beam in the above three cases. Figure 5 (c, f, i) are respectively the light intensity distribution diagrams of the outgoing beam passing through the polarizer with the horizontal polarization direction and the quarter wave plate with the fast axis at 45 degrees from the horizontal direction in the above three cases. In practical applications, the phase φ of the phase plate 2 can be pixelated and dynamically controlled in real time through a phase spatial light modulator or other optical elements. If the phase of the square area in Figure 5 (a, d, g) is reduced to a single pixel, the polarization corresponding to the pixel will also change accordingly.

As another embodiment, the phase parameter

in,

Are the convergence angle and azimuth angle of the first objective lens 5, k=2π/λ, incident light wavelength λ=633nm, m=20, and the low-pass filter 6 adopts a pinhole or light _{with an effective clear aperture radius r 0 =310μm.} Lanna realized. The position of each component, as well as the light path passing direction and sequence are the same as those in the above embodiment, and will not be repeated here. As a result, as shown in FIG. 6, different phase plates 2 can emit light beams with different polarization distributions from the objective lens 7. Specifically, when the phase distribution of the phase plate 2 is as shown in Fig. 6(a), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the vertical linearly polarized light beam in the square area; when the phase distribution of the phase plate 2 is as shown in Fig. 6(d) , The light beam emitted by the objective lens 7 is composed of the background right-handed circularly polarized light and the square area left-handed circularly polarized light; when the phase distribution of the phase plate 2 is as shown in Figure 6(g), the light beam emitted by the objective lens 7 is composed of the background horizontal linearly polarized light and the square area right Composed of circularly polarized beams. Figure 6 (b, e, h) is the total light intensity distribution of the outgoing beam in the above three cases. Figure 6 (c, f, i) is the light intensity distribution diagram of the outgoing beam passing through the polarizer with the horizontal polarization direction and the quarter wave plate with the fast axis at 45 degrees from the horizontal direction in the above three cases. In practical applications, the phase φ of the phase plate 2 can be pixelated and dynamically controlled in real time through a phase spatial light modulator or other optical elements. If the phase of the square area in Figure 6 (a, d, g) is reduced to a single pixel, the polarization corresponding to the pixel will also change accordingly.

The device and method for adjusting the polarization state of a beam provided by the present invention include: a polarizer, a phase plate, a 4f optical system, a polarization converter, a first objective lens, a low-pass filter, and The second objective lens, the polarizer, the phase plate, the 4f optical system, the polarization converter, the first objective lens, the low-pass filter and the second objective lens share a central axis, and the 4f optical system includes a first lens and a second lens , The phase plate is located on the front focal plane of the first lens, the polarization converter is located on the back focal plane of the second lens, and the low-pass filter is located on the back focal plane of the first objective lens; external light The linearly polarized light converted into the horizontal direction by the polarizer enters the phase plate; the phase plate adjusts the phase of the linearly polarized light into a phase distribution of φ, and enters the polarized light vertically after passing through the 4f optical system The converter obtains linearly polarized light whose phase is φ and its polarization state changes in space, and its electric field distribution is:

in,

phase represents the function of extracting the phase, i is an imaginary number,

Is a constant factor, β is a phase control factor; in this embodiment, β ₀ =0, m=30; the linearly polarized light whose phase is φ and its polarization state is spatially changed passes through the first objective lens and decomposes into the first objective lens. The electric field component E _inner focused beam and the second electric field component E _outer focused beam, in which,

The first electric field component E _inner beam and the second electric field component E _outer beam enter the low-pass filter, and the second electric field component E _outer beam is filtered out, thereby obtaining the first electric field component E _inner beam; The light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution. This application uses the one-to-one correspondence between the phase and the polarization, and directly controls the polarization state of the beam through the adjustment of the phase. Since the phase of the light beam can be controlled by real-time dynamic pixelation using a phase control device, such as a phase spatial light modulator, the pixelated phase will inevitably produce a pixelated polarization output. Therefore, the present invention can realize the dynamic real-time pixel-level polarization of the beam. Control, and the energy utilization rate can be as high as 50%. Compared with the dual-beam coherent superposition method and metasurface design, and the polarization control method based on the geometric phase principle, the present invention also avoids high-precision interference systems, complex algorithms, expensive and precise processing, and the like.

It should be noted that in this article, the terms "include", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements not only includes those elements, It also includes other elements that are not explicitly listed, or elements inherent to the process, method, article, or system. Without more restrictions, the element defined by the sentence "including a..." does not exclude the existence of other identical elements in the process, method, article, or system that includes the element.

The sequence numbers of the foregoing embodiments of the present invention are only for description, and do not represent the superiority or inferiority of the embodiments.

Through the description of the above implementation manners, those skilled in the art can clearly understand that the above-mentioned embodiment method can be implemented by means of software plus the necessary general hardware platform, of course, it can also be implemented by hardware, but in many cases the former is better.的实施方式。

The above are only preferred embodiments of the present invention, and do not limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the description and drawings of the present invention, or directly or indirectly applied to other related technical fields , The same reason is included in the scope of patent protection of the present invention.

Claims (10)

1. A device for controlling the polarization state of a light beam, characterized in that the device for controlling the polarization state of the light beam comprises: a polarizer, a phase plate, a 4f optical system, a polarization converter, a first objective lens, a low-pass filter, and a first objective lens arranged in sequence. Two objective lenses, the polarizer, phase plate, 4f optical system, polarization converter, first objective lens, low-pass filter and second objective lens share a central axis,

   The 4f optical system includes a first lens and a second lens, the phase plate is located on the front focal plane of the first lens, the polarization converter is located on the back focal plane of the second lens, and the low-pass filter Located at the back focal plane of the first objective lens;

   The external light is converted into horizontal linearly polarized light through the polarizer, and enters the phase plate;

   The phase plate adjusts the phase of the linearly polarized light into a phase distribution of φ, and passes through the 4f optical system and then enters the polarization converter vertically to obtain the linearly polarized light whose phase is φ and its polarization state is spatially changed. The electric field distribution is expressed as:

   

   in,

   

   phase represents the function of extracting the phase, i is an imaginary number,

   

   Is a constant factor, β is a phase control factor;

   

   Is the generalized phase distribution,

   

   Are the convergence angle and the azimuth angle of the first objective lens, and β ₀ is the polarization control factor;

   The linearly polarized light whose phase is φ and whose polarization state is spatially changed passes through the first objective lens and is decomposed into a first electric field component E _inner focused beam and a second electric field component E _outer focused beam, which can be expressed as

   

   

   Among them, <L> and <R> represent the left and right circular polarization modes respectively;

   The first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component E _outer focused beam is filtered out, thereby obtaining the first electric field component E _inner focused beam;

   The focused light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution.
2. The control device according to claim 1, wherein the phase plate is obtained by encoding or processing and coating with a phase spatial light modulator.
3. The control device according to claim 1, wherein the generalized phase distribution

   

   _{The first electric field component E inner} focused beam and the second electric field component E _outer focused beam of the linearly polarized light whose phase is φ and its polarization state changes spatially through the first objective lens are spatially separated in the focal area of the first objective lens.
4. The control device according to claim 1, wherein the distance between the first objective lens and the second objective lens is the sum of the focal lengths of the two.
5. The control device according to claim 1, wherein the polarization converter is a liquid crystal polarization control polarization converter.
6. The control device according to claim 1, wherein the transmittance of the low-pass filter is expressed as:

   

   Among them, r ₀ is the effective aperture radius of the low-pass filter.
7. A method for adjusting the polarization state of a light beam, wherein the adjusting method is applied to the adjusting device according to any one of claims 1 to 6, and the adjusting method comprises:

   The external light is converted into horizontal linearly polarized light through the polarizer and enters the phase plate;

   The phase of the linearly polarized light is adjusted to a phase distribution of φ through the phase plate, and is perpendicularly incident to the polarization converter after passing through the 4f optical system to obtain the linearly polarized light whose phase is φ and its polarization state is spatially changed, The electric field distribution is expressed as:

   

   in,

   

   phase represents the function of extracting the phase, i is an imaginary number,

   

   Is a constant factor, β is a phase control factor;

   

   Is the generalized phase distribution,

   

   Are the convergence angle and the azimuth angle of the first objective lens, and β ₀ is the polarization control factor;

   The linearly polarized light whose phase is φ and whose polarization state is spatially changed passes through the first objective lens and is decomposed into a first electric field component E _inner focused beam and a second electric field component E _outer focused beam, which can be expressed as

   

   

   Among them, <L> and <R> represent the left and right circular polarization modes respectively;

   The first electric field component E _inner focused beam and the second electric field component E _outer focused beam enter the low-pass filter, and the second electric field component E _outer focused beam is filtered out, thereby obtaining the first electric field component E _inner focused beam;

   The focused light beam of the first electric field component E _inner passes through the second objective lens to obtain a polarized light beam with a desired polarization distribution.
8. The control method according to claim 7, wherein the generalized phase distribution

   

   _{The first electric field component E inner} focused beam and the second electric field component E _outer focused beam of the linearly polarized light whose phase is φ and its polarization state changes spatially through the first objective lens are spatially separated in the focal area of the first objective lens.
9. The control method according to claim 7, wherein the transmittance of the low-pass filter is expressed as:

   

   Among them, r ₀ is the effective aperture radius of the low-pass filter.
10. The control method according to claim 7, wherein the polarization converter is a liquid crystal polarization control polarization converter.

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